The present work investigates the performance of anode supported solid oxide fuel cells under the influence of different trace compounds. EIS (Electrochemical impedance spectroscopy) has been used to deconvolute the impedance spectra of an SOFC (Solid Oxide Fuel Cell) in order to identify the main losses. The impact of single and double contaminants on the SOFC performance has also been investigated. Typical biogas trace contaminants, obtained after a clean-up stage, such as sulfur, chlorine, aromatic compounds and siloxanes, have been taken into consideration. The results show how the ohmic contribution is almost independent of the H2S concentration. H2S acts mainly on the polarization losses and especially on the mass transport resistance. The impact of HCl on the SOFC performance is mainly connected to the charge transfer process. D4, as the model compound for siloxanes, already acts on SOFC performance at ppb(v) levels. The polarization losses have been influenced the most, and the largest increase has been recorded for the low frequency term, R-IoW, related to the mass transport resistance for naphthalene and toluene. H2S, introduced with other contaminants, causes the instantaneous deterioration of the SOFC performance and the more the types of contaminants co-fed to the SOFC, the larger the initial anode degradation. (C) 2015 Elsevier Ltd. All rights reserved.